The present invention relates to a microswitch that is actuated by acceleration.
FIG. 14 illustrates the structure of a prior art acceleration actuated microswitch 10. The switch 10 includes a casing 11, a reed switch 12, a magnetic mass 13 and spring 14.
The mass 13 is fitted about and reciprocates relative to the casing 11 between a position away from the reed switch 12 and a position close to the reed switch 12. The spring 14 retains the mass 13 at the position away from the reed switch 12.
When acceleration G, along the longitudinal axis of the casing 11, is applied to the microswitch 10, the acceleration G causes the mass 13 to slide on the casing 11 toward the reed switch 12. At this time, the magnetic force of the mass 13 closes the reed switch. The time required for the mass 13 to move to the position to turn the reed switch 12 on and the length of the period during which the reed switch 12 is on depend on the dimensional accuracy of the mass 13 and the casing 11.
However, due to limitations of the dimensional accuracy of parts, the length of the on period cannot be extended beyond a certain value, and the size of the prior art microswitch cannot be further reduced. The on time of the reed switch 12 cannot be extended by a simple modification to the construction of the microswitch 10.
Since the mass 13 slides on the case 11, an acceleration in a direction other than the longitudinal direction of the case 11 is not accurately detected. That is, if an acceleration that is inclined relative to the longitudinal direction of the case 11 is applied to the switch 10, the acceleration generates frictional force between the mass 13 and the casing 11, which prevents the mass 13 from moving smoothly. In this case, the reed switch 12 may not be closed.
In some cases, it is preferable that the sensitivity of acceleration microswitches vary in accordance with the frequency of the applied acceleration. However, the sensitivity of the prior art acceleration microswitch 10 does not vary in accordance with the frequency of applied accelerations.